Brazing cast iron casting 1x1x2ft

I bought a used industrial machine (a huge pipe threader).

It is a super nice machine in all respects and was rebuilt in 2007.


However, the reason why it was sold for nothing is that the cast iron
transmission case in it is cracked due to a past accident.


The picture, with the crack highlighted, is here:


http://igor.chudov.com/tmp/trans.jpg


You can visualize this as a rectangular casting with one corner broken
off. The three highlighted areas are in fact one crack separating only
two pieces.


The size of this is about 1x1x2ft.


What I need to do is put it back together. It would seem that the pieces could be taken out, really cleaned up,
pushed together, heated red hot, and brazed with brass.


Does that make any sense?


What would be the best approach?


Thanks

Igor, that seems like it's in the right size range for a diesel engine block repair/braze place to do it, and the basic procedure you described is just what they do. They are set up with all the preheat burners and thermal blankets to get the casting to the red heat and keep it there while brazing. I looked into getting a large floor-standing arbor press casting repaired by such a place locally, but all their workstations are really set up to do a fairly constrained size and shape. The local outfit would do a repair pretty cheaply if I had something that fit the envelope, but was not interested in doing a job that wouldn't fit in an existing workstation.

An oversized BBQ grill and a OA torch..... that 2 foot size is gonna be a bugger. Heck, It won't even fit into a trash can. ;-)

Lots of threads here on welding or brazing iron castings. This one is nothing special. All parts have to stripped off lest pre-heat damage them. Vee cracks but leave a narrow land of fracture surface for alignment. Casting may warp a bit, requiring re-alignment of bores or other precision locating surfaces, or maybe not.

Being it looks like that broke under load, I would disassemble, clean it up, then clamp in place and try to drill and tap bolts, as large and as many as possible, in a few locations to mechanically hold it securely enough to withstand the loads it endures, then braze over all that so nothing can work loose. Could also machine in or scab on and bolt steel reinforcement plates and braze over those.

ichudov,sir,

That gear box looks to be a very simple arrangement that is bolted in place. If it were mine and expected it to deliver dependably I think it would be easy to fabricate a new one from steel and machine it for the gear shafts using bronze plain bearings. If you don't have a mill the machining cost would be warranted for a producing machine.

Bob....not the cat.

Since its useless as is the first thing I would do is strip it down completely and post a couple of pictures. Pressure wash it well first. It will be much easier to assess the situation with a better look at the part and the break. Put a rule or tape measure across an unimportant piece for scale.

I have to agree with Mike C. on repair. Vee it out but leave enough area to positively locate the part. Then drill and tap for screws and screw the casting back together. Then braze it back together, including the screws.

This is probably a two men and a boy sized operation. If I were doing it I would want a wood fire for initial preheat, a weed burner to maintain preheat, some fire resistant insulation to maintain the heat, two acetylene torches with rosebuds, 10-20 lbs of bronze rod, about 4 hours, and enough insulation to cover the part to allow slow cooling.